The present invention relates to a combustion state diagnosing system for diagnosing the combustion state of a multiple-cylinder engine and, more particularly, to a combustion state diagnosing system and a combustion state diagnosing method capable of accurately finding the occurrence of a misfire.
If an engine misfires, expected energy of combustion cannot be produced, the output of the engine decreases, and unburned gasses are discharged into an exhaust system to cause various problems. For example, the unburned gasses discharged into the atmosphere cause air pollution. Furthermore, part of the unburned gases burn in a catalytic unit included in the exhaust system and heats the exhaust system at an abnormally high temperature, which may possibly cause the catalytic unit to melt. If the catalytic unit melts, the exhaust gas cannot be purified, causing air pollution.
To prevent such air pollution, the ARB (Air Resources Board) of California, USA provides by regulations that misfires shall be detected and, if the frequency of misfires exceeds a predetermined value, malfunction codes shall be stored and information shall be given to that effect to the driver by lighting up a malfunction indicator light. A threshold frequency of misfires in such a case must be determined taking into consideration a frequency detrimental to the exhaust gas (frequency of misfires in 1000 rotations of the crankshaft of the engine) and a frequency detrimental to the catalytic unit (frequency of misfires in 200 rotations of the crankshaft of the engine). The concrete value of the threshold frequency of misfires is dependent on the type of the vehicle and the property of the exhaust gas provided by relevant regulations. For example, about 2% of a low frequency of misfires must be sensed, which corresponds to 80 misfires per 1000 rotations of the crankshaft of an 8-cylinder engine. Suppose that misfires occur in such a frequency in one cylinder, a malfunction indicator light must be turned on if the frequency of misfires in 500 ignition cycles is eighty. The upper limit of an operating range in which misfires must be detected was raised from an upper limit on the order of 3000 rpm to the maximum engine speed on the order of 6000 rpm. The regulations require the detection of misfires in a wide range of a no-load condition to a full-load condition.
The following prior arts are available for detecting misfires in engines.
Disclosed in Japanese Patent Laid-open No. 4-19344 is an apparatus which detects abnormal combustion on the basis of the magnitudes of components for frequencies determined through the frequency analysis of engine speed information.
Disclosed in Japanese Patent Laid-open No. 6-58196 is an apparatus for detecting misfires and judging cylinders in which misfires occurred, in which the apparatus comprises a torque measuring means for measuring the instantaneous magnitude of the output torque of an engine, a specific frequency component extracting means for extracting a predetermined specific frequency component from the measured output torque measured by the torque measuring means, a misfire pattern judging means for judging if any misfire occurred in a cylinder on the basis of the specific frequency component and judging a misfire pattern if a misfire occurred, a storage means for storing data representing the relation between a misfired cylinder and the phase shift of the specific frequency component for each misfire pattern, and a misfired cylinder judging means for judging a misfired cylinder by comparing the phase shift of the specific frequency component and a phase shift stored in the storage means according to the judged misfire pattern.
Disclosed in Japanese Patent Laid-open No. 6-26996 is a technique for judging a combustion state from the variation of rotating speed. This known technique in order to eliminate the error factor due to the error caused by the measuring system, measures a time necessary for the crankshaft to turn through a predetermined angle, extracts a characteristic component from values of combustion state parameter measured every one or more rotations, calculates a combustion state parameter by using the extracted characteristic component or on the basis of an extracted characteristic component extracted from a value for the necessary time in one or a plurality of rotations, and judges the combustion state of each cylinder on the basis of the combustion state parameter.
Japanese Patent Laid-open No. 4-19344 discusses misfire detection when misfires occur successively (every ignition cycle), but does not discuss the detection of misfires that occur at a low frequency necessary to meet the above-mentioned regulations. Since the two-rotation period component of the output of the rotation signal output means (a component of a frequency equal to a quarter of a frequency fTDC corresponding to the ignition period of a specific cylinder in Japanese Patent Laid-open No. 4-19344, which is equal to two-rotation period component for two rotations of the crankshaft of the engine) or a component of a period equal to a integral multiple of period (a frequency of fTDC/4 m, m is a natural number) is extracted in a fixed period, the extraction frequency varies according to the engine speed. Therefore, the power of a frequency component extracted while the engine speed is momentarily varying disperses on frequency basis and hence the accuracy in misfire detection is reduced. Since a frequency analysis window (sampling frequency) must be longer than the period of a component to be extracted, sampling must be repeated many times. The period of rotation is especially long while the engine speed is low and hence the frequency analysis window must be of a long time. The period of rotation is short while the engine speed is high, the frequency analysis window is, for example, for at least several tens rotations. Therefore, if misfires occur at a low frequency, the frequency component produced by misfires is small and it is difficult to discriminate between misfiring and normal firing. Since specific frequency components must be extracted from many sampled data, load on the arithmetic unit increases and a special, expensive CPU or the like will be necessary.
Japanese Patent Laid-open No. 6-58196 discusses cases where a specific cylinder misfires every ignition cycle, but nothing is taken into consideration about the detection of misfires that occur at a low frequency necessary to meet the above-mentioned regulations. Also, expensive torque measuring means is required. Periodic extraction of rotation xc2xd-order and 1-order components from the output signal of the torque sensor entails the above-mentioned technical problems.
A combustion state detecting technique based on rotating speed information does not need any expensive sensor and is prevalently used for detecting the combustion state of automobile engines. However, it is difficult to detect the combustion state of an engine having a large number of cylinders or a large rotative inertia in a high accuracy because the engine speed varies scarcely when a misfire occurs while the engine is operating at a high engine speed under a low load.
Experiments proved that it is difficult to achieve accurate misfire detection by a prior art proposed by the applicant of the present patent application in Japanese Patent Laid-open No. 6-26996 when an 8-cylinder engine is operating at 6000 rpm under a low load.
It is an object of the present invention to provide a low-cost combustion state diagnosing system and a combustion state diagnosing method capable of accurately detecting misfires which occur at a low frequency while a multiple-cylinder engine is operating at a high engine speed under a low load.
The object can be achieved, when diagnosing combustion state, by extracting specific rotation period component of a period synchronous with rotation from a combustion state parameter for at least two rotations, and judging combustion state on the basis of the extracted specific rotation period component. The combustion state parameter may be the engine speed or the output torque of a multiple-cylinder engine which varies according to the combustion state of the engine. More concretely, the present invention solves the foregoing problem by the following system.
A combustion state diagnosing system for diagnosing the combustion state of a multiple-cylinder engine by measuring a parameter of combustion state varying according to the combustion state of the engine, such as engine speed or output torque, diagnosing combustion state on the basis of the parameter of the combustion state, comprises: a combustion state parameter measuring means which measures a parameter of the combustion state N times (at least once) in one ignition cycle of the multiple-cylinder engine at times corresponding to a predetermined crank angle; a specific rotation period component extracting means for extracting a specific rotation period component of a period synchronous with rotation of a crankshaft from values of the parameter of the combustion state measured by the combustion state parameter measuring means at least in two rotations of a crankshaft; and a combustion state judging means for judging the combustion state on the basis of the specific rotation period component extracted by the specific rotation period component extracting means.
In the combustion state diagnosing system, the combustion state parameter measuring means may measure necessary times T(i) each necessary for the crankshaft to turn through an angle between predetermined crank angles N times every ignition cycle of the engine, and the specific rotation period component extracting means may be provided with a high-pass filter means which filters out low-frequency components of the necessary times T(i) to calculate filtered necessary times Tf(i) to extract specific rotation period components of a period synchronous with the rotation of the crankshaft from the necessary times Tf(i).
In the combustion state diagnosing system, the high-pass filter means may filter out the components of periods longer than a time necessary for two rotations of the crankshaft of the engine.
In the combustion state diagnosing system, the high-pass filter means may calculate the difference [T(i)xe2x88x92T(ixe2x88x92N)] from the necessary times T(i) corresponding to the cylinders successive in ignition order to use the same as the filtered necessary time Tf(i).
In the combustion state diagnosing system, the measured varying values of torque may be used directly as those of the combustion state parameter.
In the combustion state diagnosing system, the specific rotation period component extracting means may be provided with an arithmetic means which extracts specific rotation period component which is a variable component of X (=Tf) of a period synchronous with the rotation of the crankshaft from the sum of the products of values of the combustion state parameter for at least two rotations of the crankshaft or Tf (=X), i.e., X(i), X(ixe2x88x921), . . . , X(ixe2x88x92c+1), where c is not less than the product of N and the number of cylinders of the engine, and at least two sets each of c pieces of weighting coefficients.
In the combustion state diagnosing system, the weighting coefficients may be set so as to extract a two-rotation period components of a period synchronous with two rotations of the crankshaft of the engine.
In the combustion state diagnosing system, the specific rotation period component extracting means may extract components synchronous with two rotations of the crankshaft of the engine. A one-rotation period component may be used.
In the combustion state diagnosing system, the specific rotation period component extracting means may extract components synchronous with one rotation of the crankshaft of the engine.
In the combustion state diagnosing system, the combustion state judging means may count the frequency of successive values of the specific rotation period component exceeding a predetermined value, may judge that a misfire occurred every ignition cycle if the count of the frequency is greater than a predetermined number, and may judge that a misfire occurred at intervals if the count of the frequency is not greater than the predetermined value.
In the combustion state diagnosing system, the specific rotation period component extracting means may include a phase calculating means for calculating the phase of the specific rotation period component, and the combustion state judging means may include a misfiring cylinder identifying means for finding the number of misfiring cylinders and/or misfiring cylinders on the basis of at least the phase of the specific rotation period component.
In the combustion state diagnosing system, the combustion state judging means may specify a pattern indicating a maximum from the sum of the products of a plurality of values of the combustion state parameters or Tf (=X), i.e., X(i), X(ixe2x88x921), . . . , X(ixe2x88x92d+1), where d is a constant, and d pieces of weighting coefficients for a plurality of predetermined patterns when it is judged that a misfire occurred, and may identify a misfiring cylinder on the basis of the maximum and the specified pattern.
Preferably, the combustion state diagnosing system further comprises a misfire counting means for counting the frequency of judgements that a misfire occurred made by the combustion state judging means in a predetermined period, and an alarm means for giving an alarm to the driver when the frequency exceeds a predetermined number and/or a misfire information storage means for storing misfire information.
The present invention provides an engine combustion state diagnosing program storage medium storing a program for measuring a combustion state parameter varying according to the combustion state of a multiple-cylinder engine, such as engine speed at which the multiple-cylinder engine is operating or output torque of the multiple-cylinder engine and judging the combustion state on the basis of the combustion state parameter; in which the program specifies measuring the combustion state parameter N times (at least once) in one ignition cycle of each cylinder at a predetermined crank angle, extracting a specific rotation period component of a period synchronous with rotation from at least the two values of the combustion state parameter, and judging the combustion state on the basis of the extracted specific rotation period component.